As part of its mission, the Opportunistic Infections Research Branch, Therapeutics Research Program, Division of AIDS, facilitates research efforts related to the discover and development of new therapies for the treatment of opportunistic infections (Ols) associated with AIDS. This includes providing contract resources for efficacy evaluations in culture and in animals, a critical component in new drug approval. Cryptosporidiosis can be life threatening in people with AIDS, and also causes a mold to severe, although self-limiting, diarrhea in immunocompetant individuals. The management of crytosporidiosis is difficult, occurrence of relapses after discontinuation of therapy is common. There is no reliable therapy or preventive agent for cryptosporidium parvum infection, regardless of immune status. Development of new, more efficacious therapeutic agents is a high research priority, yet it is hampered by 1) the difficulty of obtaining organisms for study, 2) the complexity and relative inaccessibility of in vitro and in vivo drug testing system, 3) the lack of pharmaceutical industry research in this area, and 4) the dearth of information on the biology of the parasite and the host immunologic defenses that control cryptosporidium infection. This contract will provide an important resource for expeditious evaluations of new therapies for cryptosporidiosis, and the continued improvement of in vitro and in vivo models of this infection. It will complement other activities in the Division's strategy to stimulate Ol drug discovery and development by providing these test systems that are not readily available to the scientific community. Such a resource will allow NIAID to provide critical support for investigator-initiated drug discovery for this disease, to stimulate private sector sponsorship of new drugs, to perform comparative studies of drugs and drug combinations, and contribute essential information to the design of clinical studies.